Yeah, that was posted elsewhere in the thread. I thought of it as a name specific to Usenet, as Network Decay is specific to television networks. I was hoping for a general term.

I don't think the term is specific to Usenet at all. It's genesis is in Usenet, but I've heard it used many, many times to refer to the general phenomenon that the original Eternal September was a specific instance of.

It's fine to say that, but this phenomenon is even older than the Internet. Think of the hip bar that gains a sudden influx of customers following a New York Times story. Yogi Berra remarked on this phenomenon with one of his famous quotes "Nobody goes there anymore. It's too crowded!"

Another idea related to the general phenomenon is gentrification: the cool artist colony suddenly overwhelmed with yuppies who drive up the rent, forcing the artists to move out.

Is there not a general term for this whole phenomenon?

I call it wankerisation. That is, a place, location or destination has become overwhelmed with wankers.

"I don't go to that bar anymore, it's too wankerised."

"I don't visit Facebook anymore, it's become wankerised."

"The neighbourhood is too wankerised, I can't afford to live there."

For communities and interests, I usually call it simply "getting mainstream", and the invaders "general population".

Eternal September afflicted mailing lists, too.